The present invention relates to a pneumatic vehicle tire with a symmetrical package of belt plies on a symmetrical carcass having an essentially radial steel wire and/or aramid fiber extension. An asymmetrical tread with at least three longitudinal grooves of a depth between 12 and 18 mm is provided above it. The tread is, if necessary, radially separated into cap and base. Tires of this kind are particularly designed for the application at the front and/or rear axle of non-steered multi-axle units as they are especially encountered with truck trailers and, above all, often with semitrailers.
Multi-axle units with truck trailers as well as with semitrailers are mostly non-steered, on the one hand, because of the additional initial costs of a steering mechanism of the front and/or rear axle(s), and, on the other hand, because of the additional weight of such a steering kinematic which necessarily reduces the remaining pay load due to the maximum admissible axle load that is determined by the law makers.
This problem is explained with the help of FIG. 1. This Figure illustrates schematically a three-axle semitrailer 1, the coupling point 2 of which is rotated on a circular path 3 about a central point M by a non-illustrated semitrailer truck.
At a quasi-statical view the axle unit, comprising the three non-steered axles 4, 5, and 6, seeks a--narrower--circular path about the point M while one axial that extends through the load central point G of the axle unit extends through the central point M. The position of G depends on the axle load distribution and on the axle bases. If the axle bases between front and center axle and between center and rear axle are the same, and if the axle loads are identical, G is located exactly on the center axle. This case is illustrated here. In this typical case, the two center wheels of the center axle 5 rotate exactly tangentially on a circular path about M.
Due to the missing steering mechanism, the front axle 4 and the rear axle 6, however, cannot follow an exact tangential path. Moreover, a differential angle .beta..sub.i between the tangent T.sub.i to the circular path of the inner wheel and of the circumferential direction of this wheel, i.e., a compulsory slip. The analogous effect applies to the outer wheel of the circlular path where the corresponding magnitude is marked with the index a instead of i.
On viewing the same circular path of the coupling dynamically, centrifugal forces increase by the second power with the speed. The centrifugal forces which have to be balanced out by corresponding centripetal forces. In order for the rear axle arrangement to compensate a resulting lateral force, it requires, according to the slant angle-lateral force diagram, a resulting slant angle that overlays the angle relations examined earlier quasi-statically. Thus, the center axle also assumes a slant angle, even though smaller, in relation to the circular path.
This slant angle required for producing a centripetal force at the center axle, is oriented in the same direction as the earlier discussed quasi-statical slant angle of the rear axle 6. The requirement of balancing the centrifugal forces thus leads to a further increase of the slant angle at the rear axle 6, to the build-up of a certain, correspondingly oriented slant angle at the center axle, and to a reduction of the quasi-statically determined, centrifugally acting slant angle at the front axle 4 (which, under extreme centrifugal forces in relation to the path curvature, finally will lead to a reversal of orientation in the centripetal direction).
This dynamical view shows that with non-steered multi-axle units the highest lateral force load occurs at the rear axle. Accordingly, the wear is highest at this location. In the case of three axle units, in operation, the common service life of tires of identical construction is 80,000 km at the rear axle, 120,000 km at the front axle, and 300,000 km at the center axle.
With passenger car tires it has been known to improve the cornering ability by an asymmetrical tread design that provides an enlarged positive tread portion at the outer side of the tire (the side pointing outwardly relative to the vehicle). Examples of such a design can be found in German Patent No. M 91 01 356.9 and in the advertisement in the magazine "Gummibereifung", 09/88, page 21. However, these known tire designs are not appropriate for utility vehicles and aim at something different, i.e., to increase the maximum possible transverse acceleration.
Moreover, in EP-PS 0 307 340 airplane tires have been suggested--the success of which is not known to the applicant--with which only one of the two tread halves above a symmetrical carcass and belt plies are provided with a pattern. Such tires, however, need only be designed for a service life of approximately 3,000 km and are designed for speeds that are 3 times greater.
It is, therefore, an object of the present invention to increase the service life of pneumatic vehicle tires of the aforementioned kind, especially of tires for semitrailers or trailers with non-steered multi-axle units, in particular of the rear axle.